Processes presently employed for the production of alcohol include the following operational phases: (a) fermentation of the appropriate raw materials, producing the fermented mash or .-+.beer" and (b) distillation of the "beer", obtained by fermentation whereby alcohol is produced.
In a typical known process presently used, fermentable raw material has added thereto yeasts and nutrients and then undergoes fermentation whereby a fermented mash or "beer" is obtained. The beer is then usually centrifuged and thereafter this "beer" is distilled whereby alcohol is obtained and vinasse is separated. The vinasse is a by-product and is basically a suspension of organic and mineral solid substances in water.
The characteristics of the vinasse, resulting from the alcohol production processes that are currently in use, vary according to the raw materials used and according to the process features. However, the solid organic substances contained in the vinasse are generally always approximately 80% of the solids content. The high biochemical oxygen demand (BOD) and chemical oxygen demand (COD) are due to these organic contents. The following properties are typical:
______________________________________ PROPERTIES RAW MATERIAL OF VINASSE Melasse Sugar Cane Manioc ______________________________________ BOD (g/l) 25.0 16.4 18.9 COD (g/l) 65.0 33.0 23.4 pH 4.5 4.5 4.5 ______________________________________
Historically, the vinasse slops resulting from the alcohol distillation have been thrown directly into sewers, rivers, lakes, and the like. However, the implementation of the Brazilian national plan for alcohol production now introduces the problem of adequate disposal of the vinasse, which will be produced in enormously increased quantities.
Due to the heavy pollution caused by the discharge of these slops, it will not be possible to go on throwing them directly into the natural water systems (rivers, lakes, lagoons or even the sea). Laws in the United States now prevent such discharge from being carried out. The alternative solution of transporting the resulting vinasse for use as a fertilizer on plantations and farms is not adequate, especially when large quantities of vinasse have to be disposed of. The use of vinasse as a fertilizer is suitable only for certain types of soil and in limited quantities. Moreover, spending fuel for the transportation of large volumes of vinasse represents a serious disadvantage. In order to avoid the disposal of the vinasse by simply throwing it into water or on land, the problem of eliminating this vinasse has to be solved.
An extensive research of the existing publications treating this problem has shown that there does not exist, at this time, a good solution for eliminating the vinasse. Several ways of processing the vinasse are presently being proposed by others, envolving treatment by evaporation, fermentation, etc., for subsequent use as a fertilizer or as a raw material for methane gas generation. The substances contained in the vinasse which can eventually be of use for the production of fertilizers or for other purposes are present in low concentration, as vinasse contains about 90% water. Current procedures of evaporation by heating are consequently uneconomical, as they require large expenditure of energy. According to all information reviewed, processes based on treatment by fermentation of the vinasse are also not economical.